When installing flooring it is at times desirable to have the edges of the flooring extend underneath baseboards and/or walls. To fit the flooring into this area, the wall and/or baseboard needs to be undercut at a specific height to allow the flooring to be installed underneath. Although it is possible to perform the undercutting by hand, this task is laborious and it is preferred to use a power tool. An undercut saw may be specifically designed to undercut a wall for the installation of flooring. This requires a specialized tool.
FIGS. 1 and 2 show two available undercut saw designs. FIG. 1 illustrates one of the earliest models, designed by Crain Cutter Company (Milpitas, Calif.). In this tool, an external housing 2 encloses a motor 3. Motor 3 drives a drive shaft 4. Gears at an end of armature drive shaft 4 mesh with gears on parallel spindle shaft 5 rotating shaft 5. A circular saw blade 1 is mounted on a blade mount (not visible) at the end of spindle shaft 5. The blade mount is a separate part which in conjunction with a fastener mechanically couples the blade to the spindle. Blade 1 is mounted such that the blade is held substantially parallel to the floor when the tool is positioned on the floor surface. When used herein the term circumscribe shall mean the amount of the outer circumference or toothed edge of the blade which is covered by a fixed blade guard. This fixed blade guard is attached to housing 2 and exposes less than 180 degrees of the blade for cutting. A depth gauge 9 is mounted on fixed blade guard 10 such that the depth of a cut may be selected by a user. Handles 6, 7 are used to grip the tool. The tool is activated by switch 11, in the underside of handle 7.
Similarly in the device shown in FIG. 2, a housing 2 encloses a motor 3 that rotates an armature drive shaft 4. At a distal end of shaft 4 is a gear that engages a gear on a parallel spindle shaft 5. At a distal end of spindle shaft 5 is a blade mount (not visible) for mounting a circular saw blade 1. The blade mount is a separate part which in conjunction with a fastener mechanically couples the blade to the spindle. Again the blade is essentially parallel to the floor. A fixed blade guard 10 extends around the circumference of blade 1, exposing less than 180 degrees of the blade. A depth gauge 9 allows the user to set the depth to which blade 1 will cut. Handles 6, 7 are gripped by a user to direct the tool. A switch 11 on handle 7 allows activation of the tool.
In the devices illustrated in FIGS. 1 and 2, the motor is upright and the armature drive shaft and the spindle shaft are in parallel orientation.
With reference to FIG. 3, an undercut saw employing an alternative configuration of the armature shaft and spindle shaft is shown. Again, outer housing 2 contains a motor 3 that rotates an armature drive shaft 4. Again at a terminal end of drive shaft 4 is a gear which engages a gear on spindle shaft 5. At a distal end of spindle shaft 5 is a blade mount (not visible) that allows mounting of a circular saw blade 1. The blade mount is a separate part which in conjunction with a fastener mechanically couples the blade to the spindle. In this embodiment, the armature drive shaft 4 and spindle shaft 5 are in perpendicular orientation. As in the prior tools, a depth gauge 9 is mounted to a fixed blade guard 10 to allow a user to selectively limit the depth of the cut. A handle 7 is used to direct the motion of the tool. A switch 11 on the top of the tool allows activation of the tool.
In FIG. 4, another undercut saw is illustrated. In this device, housing 2 holds a motor that turns drive shaft 4. In this embodiment, there is no spindle gear attached to shaft 4. Thus, the blade mount (not visible) for blade 4 is mechanically linked directly to drive shaft 4. On blade guard 10 there is a dust port 10a that allows dust to be channeled away from blade 1. Rounded handles 6, 7 are mounted on fixed blade guard 10. Depth gauge 9 is permanently mounted on fixed guard 10.
A number of these prior art devices are shown in U.S. Pat. Nos. 5,784,789; 5,967,013; 5,974,674 and 6,588,111 and U.S. patent application Ser. No. 09/976,483, all incorporated by reference herein.
The prior art devices have a number of drawbacks. First, the devices of FIGS. 1, 2, and 4 are unable to undercut an inside corner, as shown in FIGS. 1A, 2A, and 3A, respectively. As these saws move along a wall, the side of the saw will contact an adjacent wall before the blade reaches the corner. Also, in order to undercut an inside corner, more than 180 degrees of the circumference of the blade must be exposed, and none of these devices have this design. Thus, for two reasons, they will not undercut in the inside corner, and so the work must be done by hand. With the saw of FIG. 1, handle 6, depth gauge 9, and blade guard 10 all limit the ability to undercut inside corners. Side handle 6 and depth gauge 9 may both be removed although some time is required to remove and replace the handle. However this does not allow the saw to undercut inside corner areas because the side of the blade guard still contacts the wall, and because less than 180 degrees of the circular saw blade is exposed for undercutting.
With regard to the device of FIG. 2, the fixed blade guard is comprised of two parts, a first fixed blade guard 10 with a substantially flat top face 13 and a semi-circular back edge 14 protruding downward, which fits inside a second semi-circular skirt 15. The two circular surfaces telescope and provide a means of blade height adjustment. Skirt 15 is adjustably fixed to fixed blade guard 10 by means of bolts 16. The outside diameter of skirt 15 prevents this saw from undercutting an inside corner. Fixed blade guard 10 circumscribes more than 180 degrees of the circumference of the blade which also prohibits the blade from cutting into inside corner areas. With respect to the device of FIG. 4, both the fixed blade guard 10 and the side-mounted dust port 10a prevent the tool from accessing an inside corner area.
As shown in FIG. 3A, the device of FIG. 3 does allow undercutting of an inside corner. In this device the perpendicular orientation of the armature drive shaft and spindle shaft is more compact and allows the blade to be mounted at a more forward location on blade guard 10. Furthermore blade guard 10 is relieved along its forward edge to expose more than 180 degrees of the circumferential edge of blade 1. Blade guard 10 consists of fixed blade guard 14 with semi-circular downwardly protruding back edge 15 that fits within semi-circular height adjustment skirt 16. The two circular surfaces telescope and provide a means of height adjustment. Fixed guard 14 is adjustably fixed to skirt 16 by bolts 13.
The long back end of housing 2 provides an advantage in that it tends to counterbalance the weight of the guards and blade, preventing this kind of saw from tipping. However, this long back end makes the tool more difficult to use in tight spaces, such as closets. Furthermore, the drive system consisting of a spindle gear perpendicular to an armature gear is not effective for generating low RPMs or high torque. Thus this type of saw can tend to bog down and overheat in operation.
With respect, the device of FIG. 1, and of FIG. 4 have a fixed blade guard which consists of a single semi-circular part with a downwardly protruding back edge. However, more recent designs such as the devices of FIGS. 2 and 3 have a fixed blade guard which is mechanically coupled to a height adjustment skirt. When used herein, the term fixed blade guard may refer to either a) a device with a fixed blade guard consisting of a single part or b) a device with a fixed guard and a height adjustment skirt. Additionally, a feature described as being part of or attached to the height adjustment skirt may be considered as part of the fixed blade guard, as this is one assembly designed to perform the function of a fixed blade guard.
Some of the features, such as the dust port, would be more useful if these features could be accommodated into a device that was able to undercut inside corners and could also provide more adequate torque.
In addition to the problem of cutting the inside corner, all of the prior devices have less than ideal handles. The handles of FIG. 1 are sufficient for control of the tool and allow sufficient pressure for direction of the tool. However if the user is in a squatting position near the floor (the preferred position for use of this tool), the wrist of the user is bent back at an angle to grip handle 7. In addition, the position of the handles tends to make the user put downward pressure on the tool, making the desired sideways motion less comfortable. For the undercut saw in FIG. 2, the handle position is also poor. Handle 7 requires that a user grip the handle such that a trigger finger is on switch 11. This requires that in use the user bend one wrist back at an uncomfortable angle. This again reduces the efficiency of the tool.
In the undercutting saw of FIG. 3, only a single handle is included. The user must keep a separate hand on the housing of the tool. The handle 7 is attached to the housing by a pair of bolts 12 that allow the handle to be adjustably positioned. However this adjustable positioning makes the handle prone to rotate forward, especially as force on the handle is exerted during cutting. In addition, the handle is gripped from the top, which is a less than efficient position for the desired sideways movement of the tool in operation. During use of the device housing 2 is heated by motor 3 and becomes uncomfortable as a gripping surface. To effectively direct the tool during operation, most of the force directing the tool is from the user gripping the sides of housing 2 and moving the tool along the wall. Finally, the handles 6, 7 of FIG. 4 are also awkward, requiring a user to grip ball like structures. These handles are gripped from the top requiring a clawlike extension of all fingers over the rounded handles.
Placement of the switch is also a concern. Ideally, the switch would be placed such that it can be easily accessed by the user's trigger finger, allowing rapid shutoff of the tool should the need arise. In FIG. 1, the placement of trigger switch 11 on handle 7 requires the user to grip handle 7 directly from above. This tends to put downward pressure on the tool, which makes the desired sideways motion of the tool along a wall more difficult.
In FIG. 2, the orientation of the handle 7 is parallel to the floor. When the user grasps this handle their wrist is naturally bent. Thus as the user attempts to apply pushing force on handle 7 the sensation is one of having one's wrist bent further backwards, which is quite uncomfortable. Furthermore, to activate the trigger-type switch 11 the user must pull it with the trigger finger. Thus, the hand is pushing forward while also pulling a switch backward at the same time, which is awkward. Moreover, the added tension in the wrist created by the pulling action of the trigger finger creates even greater discomfort in the wrist.
When using the device of FIG. 3, the user grips handle 7 with one hand and places the other hand on the housing. The spring loaded switch 11 is activated by the placing a thumb on the trigger and pushing forward, and deactivated by removing the thumb. Because the thumb is not on the housing, it does not assist in gripping, which is not effective for transferring force. In FIG. 4, the switch 11 for the device is on the housing, not on the handles 6, 7. This means that to turn off the device a user must let go of at least one handle. This makes shutting off the device during an emergency take more time. This is not ideal during an emergency, especially if the user has lost some control of the tool.
Many features which are preferred in the design of an undercutting saw make it likely to tip over, which is a safety hazard. In order to expose as much of the forward circumference of the blade as possible, it is preferable to mount the motor housing as far forward as possible on the fixed blade guard. Thus, the bulk of the weight is centered on a cantilevered area. Furthermore, recent designs which can fully undercut inside corners require that more forward support from the fixed blade guard be removed. Lastly, in a device with a motor that employs parallel drive and spindle shafts, the motor is taller and thereby generates more leverage that tends to cause tipping. However, a device with a parallel drive and spindle shaft is preferred due to the greater torque these motors generate from lower RPM.
It is an object of the invention to provide a undercut saw with improved, ergonomic handles.
It is a further object to provide an undercut saw with a dust port that still allows inside corner cutting.
It is a further object of this invention to provide an undercut saw with a depth gauge with an operating surface that positions the saw for optimal utilization of its dust control port.
It is a further object of this invention to provide an undercut saw with a drive shaft parallel to a spindle shaft with a fixed blade guard which can expose greater than 180 degrees of the blade circumference.
It is a further object of this invention to provide a saw with a stabilizer that can help to reduce tipping.